Download DIVERSITY HYPOTHESIS

Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
IV. Succession
V. Biodiversity: Patterns and Processes
A. The Species-Area Relationship
B. The Latitudinal Trend in Diversity
1. The patterns
Amphibians
Lizards
Snakes
Moss
Bivalves
Ants
Lizards
Birds
Marine Gastropods
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
IV. Succession
V. Biodiversity: Patterns and Processes
A. The Species-Area Relationship
B. The Latitudinal Trend in Diversity
1.
The patterns
2.
Potential Causes
a. energy-diversity hypothesis
"Bottom-Up" - more Energy, more sp.
- quantitative effects
"Bottom-Up" - more Energy, more sp.
- quantitative effects
a. ENERGY – DIVERSITY HYPOTHESIS
PET = amount of
water that a plant
would lose to the
environment;
increases with
radiation and
decreases with
increasing humidity.
"Bottom-Up" - more Energy, more sp.
- qualitative effects: energy increasing types of
diversity
The tropics not only have MORE productivity, they have more KINDS of
productivity – more types of plants, allowing greater specialization by more
types of animals. We tend to see this diversity evolving by sister species
using slightly different resources. This should make sense; sister species
are probably very similar, and so they would have to partition some
important resources in order to coexist without competitive exclusion.
This diversity evolves by sister species using slightly different resources.
This should make sense; sister species are probably very similar, and so
they would have to partition some important resources in order to coexist
without competitive exclusion.
"Bottom-Up" - more Energy, more sp.
"Top-Down" – more energy, more predators,
less, competitive exclusion at each trophic
level.
"Bottom-Up" - more Energy, more sp.
"Top-Down" - more predators, less
competitive exclusion.
"Faster Evolution" and speciation
"Faster Evolution" and speciation
Rohde, K. 1992. Latitudinal Gradients in Species Diversity: The Search
for the Primary Cause. Oikos 65: 514-527.
Mutation rates are increased by radiation and heat - so mutation
rates should be higher in the tropics...Confirmed
developmental rate is faster at higher temps, so generation time
should be shorter.... Confirmed
So, with greater variation and more rapid generational turnover,
responses to selection (and other evolutionary agents) should
be more rapid in the tropics... divergence and speciation should
be more rapid in the tropics.
"Faster Evolution" and speciation
Weir, JT, and D Schluter. 2007. The Latitudinal Gradient in Recent
Speciation and Extinction Rates of Birds and Mammals. Science 315:
1574 - 1576.
Compared pairs of sister bird and mammal taxa in the tropics and
temperate zone. Compared DNA, and estimated time since divergence
for these pairs. Temperate pairs of birds and mammals had MORE
RECENT divergence times than pairs of tropical species.
BIRDS
Time since divergence of
species pairs.
Age of intraspecific
haplotype variation.
Age of deepest phylogroup
splits
all relationships are strongly
significant (p < 0.001)....
MAMMALS
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
IV. Succession
V. Biodiversity: Patterns and Processes
A. The Species-Area Relationship
B. The Latitudinal Trend in Diversity
1.
The patterns
2.
Potential Causes
a. energy-diversity hypothesis
b. habitat heterogeneity – diversity hypothesis
Andes, Equator
Rockies, 60 N
- Area Effect - the tropics have more area
than ecosystems at higher latitudes.
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
IV. Succession
V. Biodiversity: Patterns and Processes
A. The Species-Area Relationship
B. The Latitudinal Trend in Diversity
1.
The patterns
2.
Potential Causes
a. energy-diversity hypothesis
b. habitat heterogeneity – diversity hypothesis
c. Intermediate disturbance hypothesis
Diversity is Maximized at Intermediate
Disturbance (Connell, 1978).
Diversity
Disturbance
- "Disturbance" is removal of biomass...
- frequency
- intensity
- areal extent
Diversity
Disturbance
- Why is diversity maximized in the middle?
Competitive exclusion in
very stable habitats
Diversity
Disturbance
- Why is diversity maximized in the middle?
No competitive exclusion because disturbance
keeps populations low, but doesn't cause
extinctions.... lots of colonists coexist...
Diversity
Disturbance
- Why is diversity maximized in the middle?
Environment is too harsh;
only species that can survive
the disturbance persist...
Diversity
Disturbance
V. Biodiversity: Patterns and Processes
A. The Species-Area Relationship
B. The Latitudinal Trend in Diversity
1.
The patterns
2.
Potential Causes
a. energy-diversity hypothesis
b. habitat heterogeneity – diversity hypothesis
c. Intermediate disturbance hypothesis
d. Environmental stability hypothesis
end of last glacial - 10,000 years ago
So temperate regions
have not had enough
time to exploit all the
available niches
opened by glacial
retreat.
- BUT.. still a global impact on climate...
V. Biodiversity: Patterns and Processes
A. The Species-Area Relationship
B. The Latitudinal Trend in Diversity
1.
The patterns
2.
Potential Causes
a. energy-diversity hypothesis
b. habitat heterogeneity – diversity hypothesis
c. Intermediate disturbance hypothesis
d. Environmental stability hypothesis
3. Cradle or Museum?
Cradle or museum?
David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics:
Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102106.
Diversity is a function of speciation rate, extinction rate, and immigration rate
(range expansion into that region).
HIGHER SPECIATION RATE
LOWER EXTINCTION RATE
Cradle or museum?
David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics:
Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102106.
Diversity is a function of speciation rate, extinction rate, and immigration rate
(range expansion into that region).
"Out of the tropics" model
Cradle or museum?
David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics:
Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102106.
Looked at the origin of bivalve taxa (genera) in tropics and beyond
Genera first appearing in the Pleistocene (2mya)
Cradle or museum?
David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics:
Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102106.
Genera first appearing in the Pliocene (5 mya)
Cradle or museum?
David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics:
Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102106.
Genera first appearing in the Miocene (23 mya)
Cradle or museum?
David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics:
Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102106.
SO: The tropics may be both cradle and museum. And that begs the question
regarding divergence rates... could pairs of species in temperate zone with recent
common ancestors have a tropical origin?
V. Biodiversity: Patterns and Processes
A. The Species-Area Relationship
B. The Latitudinal Trend in Diversity
C.
Trend in Diversity over Geological Time
Geological Time
- diversity increases through time
- there are periodic mass
extinctions, followed by faunal
recovery
Geological Time
Patterns in Fish Diversity
Competitive replacement
seems likely, as do adaptive
radiations of competitively
successful group.
Geological Time
Patterns in Tetrapod Diversity
Geological Time
Patterns in Plant Diversity
- innovation: new “adaptive zone” colonized
- radiation – explosion of species colonizing new
areas and exploiting new environments in this new way
- competitive contraction? – winners exclude others…
Mechanisms:
- How/why is a new adaptive zone colonized?
Mechanisms:
- How/why is a new adaptive zone colonized?
1. Evolve a new way of life that allows the organism to
use new resources, or old resources in a new way (adaptations
to land… adaptations for flight…)
2. Colonize an uninhabited area (islands) – these are
“ecological vacuums”, too…
3. Be released from competition by mass extinction of
competitors…
Geological Time
But predation has been important, too.
This is Spriggia, thought to be a
soft-bodied arthropod precursor.
Animals of the
Vendian Period: 650543 mya
These are Cnidarians stinging predators
Geological Time
But predation has been important, too.
Animals of the Cambrian Period: 543-490 mya
Predation - selects
for anti-predator
traits in prey
Hard parts evolve... leading to a
burst in preserved specimens
Geological Time
Mutualisms are
important, too
Cretaceous
beetles
Ants,
bees,
wasps
flies
Flowering Plants (Angiosperms) and Insect
Pollinators
Butterflies
and moths
Conclusion:
There are a range of factors that probably contribute differentially depending on
the taxon.
Climate
Evolutionary
Processes
Trophic
Relationships
History
DIVERSITY